There is a series of abundant, homodisperse, long lived, mostly nuclear, low molecular weight RNA species in vertebrate cells (other than transfer RNAs and 5 S ribosomal RNA), whose role in the cell is unknown. This project deals with the study of the mature species of some of these RNAs in mammalian cells. One of current interest in the nuclear-cytoplasmic partition of these RNAs, particularly after non-aqueous cell fractionation. Another interest is in the apparent particle association of some of these RNAs, as there are indications that some of these RNA species may be associated with the heterogeneous nuclear RNA particles. The metabolic stability of some of these RNAs has been studied in growing heteroploid cells; we would like to examine their stability in resting and growing diploid cells. It appears that there is a large number of genes coding for some of these RNAs, especially C and D. We wish to reexamine this point, also attempting to identify the chromosomes involved, by in situ hybridization. The effect of purified RNA species in cell-free systems of transcription or translation will be tested.